Decline of circadian photosensitivity associated with retinal degeneration in CBA/J-rd/rd mice.
Although it is well known that visual image formation is mediated by rods and cones, photoreceptors implicated in entrainment of circadian rhythms remain unknown. In our previous study, 12-week-old CBA/J-rd/rd mice were found to show decreased sensitivity in circadian photoreception. Because rd gene induces different age-related degeneration of cones and rods, we have examined age-related changes in the sensitivity to a light pulse for phase-shifting the locomotor activity rhythms in CBA/J-rd/rd mice. Since mice have middlewave-sensitive cones (M-cone, 510 nm) and shortwave-sensitive cones (S-cone, 360 nm), a 15-min monochromatic light pulse (501.6 or 359 nm; 10 microW cm(-2) s(-1)) was given at circadian time (CT) 16, 2 weeks after being transferred to constant darkness (DD) and the magnitude of phase shift was determined. The amount of phase shift by a green light pulse (501.6 nm) gradually declined from 8 to 16 weeks after birth and the similar tendency was also observed on a UV pulse (359 nm). The similar pattern of age-related decline in the number of cones and circadian photosensitivity in CBA/J-rd/rd mice suggest that cones are involved in the circadian photoreception in mice.
Yoshimura
T
T
Department of Animal Physiology, School of Agricultural Sciences, Nagoya University, Japan. takashiy@agr.nagoya-u.ac.jp
Ebihara
S
S
D000704:Analysis of Variance; D000818:Animals; D002940:Circadian Rhythm / Q000502:physiology*; D051379:Mice; D008808:Mice, Inbred CBA; D010786:Photoreceptor Cells / Q000502:physiology*; D010787:Photosensitivity Disorders / Q000503:physiopathology*; D012162:Retinal Degeneration / Q000503:physiopathology*; D014466:Ultraviolet Rays